1. Field of the Invention
This invention relates generally to a pressure activated shut-off valve and, more particularly, to a pressure activated shut-off valve for a cryogenic hydrogen storage tank where the hydrogen pressure in the tank is used to open the valve.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cells and hydrogen operated internal combustion engines as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing hydrocarbon operated internal combustion engines.
In an automotive fuel cell application, the hydrogen is sometimes stored in a cryogenic tank on the vehicle, where the hydrogen is a liquid at very cold temperatures, such as −253° C. The cryogenic tank typically includes an inner tank and an outer tank with a vacuum and a multi-insulation (MLI) layer therebetween to limit heat penetration into the inner tank to maintain the liquid hydrogen in its super cold state.
A cryogenic shut-off valve is typically provided in a supply line from the tank that is opened during operation of the fuel cell system to provide hydrogen thereto, and is closed when the system is shut-down. Because the liquid hydrogen is very cold, certain design requirements need to be addressed so that the valve does not leak at such low temperatures created by the liquid hydrogen flowing through the valve during vehicle operation. When the system is not drawing hydrogen from the tank and the cryogenic shut-off valve is closed, then the valve may warm up to ambient temperatures. Thus, high forces are required to maintain the shut-off valve in the closed position to prevent leakage over a wide range of temperatures.
Shut-off valves of the type discussed above should provide for the precise opening and closing of the hydrogen supply line, minimal part count, minimal power requirements, minimal heat intrusion into the tank and fail-safe operation.
Electromagnetic valves are one known option for cryogenic shut-off valves of this type. A large spring holds the valve in the closed position with enough force to prevent hydrogen leaks, as discussed above. However, because of the large forces required to maintain the valve in the open position against the bias of the spring, the electromagnet requires a lot of energy. Also, the size and weight of a large electromagnet is a design concern. Certain electromagnetic shut-off valves utilize a pilot pressure to reduce the opening force of the valve. However, such valves require two seat surfaces that may significantly increase the potential for leakage.
It is known to overcome some of the limitations of an electromagnetically actuated valve by providing a pneumatically actuated valve that uses air pressure to open the shut-off valve against the spring force. The pneumatic actuated valve requires an air compressor that provides the air pressure to open the valve against the spring force. Pneumatically controlled valves do not have the drawbacks of the electromagnetically control valves that require high currents, but do have other design concerns that need to be addressed. These concerns include the requirement of a compressor, humidity control for preventing freezing, filtering dust particles, etc.